Our companys' goal is to create and commercialize a modular, immediate fit, transtibial prosthesis system at a fraction of the cost of conventionally manufactured devices. Our product will be mass produced using the latest injection molding techniques with advanced materials that duplicate the strength of metal at a fraction of the cost. This system will be immediately fit on the residual limb and aligned for optimal gait without specialized tools or facilities. The advanced prototype incorporates a new socket that uses a buckle system ? similar to a ski boot ? with a rear entry panel that allows for fine adjustments to optimize fit and comfort. Our new design has been well received by subjects to date and biomechanical testing revealed gait patterns similar to those with their conventional devices. The goals and aims for Phase I were fully met and we demonstrated the feasibility of immediate fit prosthetics. Phase II funding is now necessary to fully test, develop, and commercialize our novel device ?a self-contained transtibial prosthesis system that is immediately fit and provides a high level of comfort and functionality. Our collaboration with Advanced Design Concepts (ADC) and their engineering team has been highly successful in developing our current product. The principal business interest in this study iFIT Prosthetics, LLC is well poised to carry out te aims of this Phase II project under the direction of the primary investigator (Dr. Dillingham). Thi proposed two year project will bring our prototype product to the point of, marketing, sales, and commercialization. The specific aims of this Phase II project are threefold. First we will test 30 unilateral transtibial amputees at more intense levels of ambulation, assessing comfort, ease of use and stability with our device. Second, ADC Engineering will fabricate metal templates for injection molding our prototypes and then produce 50 transtibial prostheses. Third, ADC Engineering will conduct International standards testing on our devices to insure they exceed international standards for strength and durability. Concurrent with this testing and manufacture, iFIT Prosthetics will develop web-based sales capabilities and educational materials for prosthetists that will use our product as part of a commercialization plan. The market for this device is quite large internationally and in the United States. Our future customers are many and include; i) amputees from impoverished countries for whom conventional manufacture and prosthesis fitting are cost prohibitive, ii) amputees who experience volume changes in their residual limb shortly after amputation or because of heart and renal diseases, and iii) pediatric amputees who are growing and need an adjustable, comfortable prosthesis. Currently, there are no commercially available devices such as ours on the market. Our product will be introduced at a considerable cost advantage relative to standard prostheses, yet is equally as comfortable and functional. The concept iFIT Prosthetics is advancing?immediate fit devices? could well lead to changes within the prosthetics industry.